聊聊RocketMQMessageListener的实现机制

序

本文主要研究一下RocketMQMessageListener的实现机制

示例

@Service
@RocketMQMessageListener(nameServer = "${demo.rocketmq.myNameServer}", topic = "${demo.rocketmq.topic.user}", consumerGroup = "user_consumer")
public class UserConsumer implements RocketMQListener<User> {
    @Override
    public void onMessage(User message) {

        System.out.printf("######## user_consumer received: %s ; age: %s ; name: %s \n", message, message.getUserAge(), message.getUserName());
    }
}

实现了RocketMQListener接口的类，再配合@RocketMQMessageListener注解就可以实现对rocketmq消息的消费

RocketMQListener

rocketmq-spring-boot/src/main/java/org/apache/rocketmq/spring/core/RocketMQListener.java

public interface RocketMQListener<T> {
    void onMessage(T message);
}

RocketMQListener接口定义了onMessage方法

RocketMQMessageListener

rocketmq-spring-boot/src/main/java/org/apache/rocketmq/spring/annotation/RocketMQMessageListener.java

@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface RocketMQMessageListener {

    String NAME_SERVER_PLACEHOLDER = "${rocketmq.name-server:}";
    String ACCESS_KEY_PLACEHOLDER = "${rocketmq.consumer.access-key:}";
    String SECRET_KEY_PLACEHOLDER = "${rocketmq.consumer.secret-key:}";
    String TRACE_TOPIC_PLACEHOLDER = "${rocketmq.consumer.customized-trace-topic:}";
    String ACCESS_CHANNEL_PLACEHOLDER = "${rocketmq.access-channel:}";

    /**
     * Consumers of the same role is required to have exactly same subscriptions and consumerGroup to correctly achieve
     * load balance. It's required and needs to be globally unique.
     *
     *
     * See <a href="http://rocketmq.apache.org/docs/core-concept/">here</a> for further discussion.
     */
    String consumerGroup();

    /**
     * Topic name.
     */
    String topic();

    /**
     * Control how to selector message.
     *
     * @see SelectorType
     */
    SelectorType selectorType() default SelectorType.TAG;

    /**
     * Control which message can be select. Grammar please see {@link SelectorType#TAG} and {@link SelectorType#SQL92}
     */
    String selectorExpression() default "*";

    /**
     * Control consume mode, you can choice receive message concurrently or orderly.
     */
    ConsumeMode consumeMode() default ConsumeMode.CONCURRENTLY;

    /**
     * Control message mode, if you want all subscribers receive message all message, broadcasting is a good choice.
     */
    MessageModel messageModel() default MessageModel.CLUSTERING;

    /**
     * Max consumer thread number.
     * This property control consumer thread pool executor maximumPoolSize see
     * {@link ConsumeMessageService#updateCorePoolSize(int)}
     * @see <a href="https://github.com/apache/rocketmq-spring/issues/546">issues#546</a>
     */
    int consumeThreadMax() default 64;

    /**
     * consumer thread number.
     */
    int consumeThreadNumber() default 20;

    /**
     * Max re-consume times.
     *
     * In concurrently mode, -1 means 16;
     * In orderly mode, -1 means Integer.MAX_VALUE.
     */
    int maxReconsumeTimes() default -1;

    /**
     * Maximum amount of time in minutes a message may block the consuming thread.
     */
    long consumeTimeout() default 15L;

    /**
     * Timeout for sending reply messages.
     */
    int replyTimeout() default 3000;

    /**
     * The property of "access-key".
     */
    String accessKey() default ACCESS_KEY_PLACEHOLDER;

    /**
     * The property of "secret-key".
     */
    String secretKey() default SECRET_KEY_PLACEHOLDER;

    /**
     * Switch flag instance for message trace.
     */
    boolean enableMsgTrace() default false;

    /**
     * The name value of message trace topic.If you don't config,you can use the default trace topic name.
     */
    String customizedTraceTopic() default TRACE_TOPIC_PLACEHOLDER;

    /**
     * The property of "name-server".
     */
    String nameServer() default NAME_SERVER_PLACEHOLDER;

    /**
     * The property of "access-channel".
     */
    String accessChannel() default ACCESS_CHANNEL_PLACEHOLDER;
 
    /**
     * The property of "tlsEnable" default false.
     */
    String tlsEnable() default "false";

    /**
     * The namespace of consumer.
     */
    String namespace() default "";

    /**
     * Message consume retry strategy in concurrently mode.
     *
     * -1,no retry,put into DLQ directly
     * 0,broker control retry frequency
     * >0,client control retry frequency
     */
    int delayLevelWhenNextConsume() default 0;

    /**
     * The interval of suspending the pull in orderly mode, in milliseconds.
     *
     * The minimum value is 10 and the maximum is 30000.
     */
    int suspendCurrentQueueTimeMillis() default 1000;

    /**
     * Maximum time to await message consuming when shutdown consumer, in milliseconds.
     * The minimum value is 0
     */
    int awaitTerminationMillisWhenShutdown() default 1000;

    /**
     * The property of "instanceName".
     */
    String instanceName() default "DEFAULT";
}

RocketMQMessageListener注解定义了consumerGroup、topic、selectorType、selectorExpression、consumeMode、messageModel、consumeThreadMax、consumeThreadNumber、maxReconsumeTimes、consumeTimeout、replyTimeout、accessKey、secretKey、enableMsgTrace、customizedTraceTopic、nameServer、accessChannel、tlsEnable、namespace、delayLevelWhenNextConsume、suspendCurrentQueueTimeMillis、awaitTerminationMillisWhenShutdown、instanceName属性

RocketMQMessageListenerBeanPostProcessor

rocketmq-spring-boot/src/main/java/org/apache/rocketmq/spring/annotation/RocketMQMessageListenerBeanPostProcessor.java

public class RocketMQMessageListenerBeanPostProcessor implements ApplicationContextAware, BeanPostProcessor, InitializingBean {

    private ApplicationContext applicationContext;

    private AnnotationEnhancer enhancer;

    private ListenerContainerConfiguration listenerContainerConfiguration;

    @Override
    public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
        return bean;
    }

    @Override
    public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
        Class<?> targetClass = AopUtils.getTargetClass(bean);
        RocketMQMessageListener ann = targetClass.getAnnotation(RocketMQMessageListener.class);
        if (ann != null) {
            RocketMQMessageListener enhance = enhance(targetClass, ann);
            if (listenerContainerConfiguration != null) {
                listenerContainerConfiguration.registerContainer(beanName, bean, enhance);
            }
        }
        return bean;
    }

    @Override
    public void setApplicationContext(ApplicationContext applicationContext) throws BeansException {
        this.applicationContext = applicationContext;
    }

    @Override
    public void afterPropertiesSet() throws Exception {
        buildEnhancer();
        this.listenerContainerConfiguration = this.applicationContext.getBean(ListenerContainerConfiguration.class);
    }

    private void buildEnhancer() {
        if (this.applicationContext != null) {
            Map<String, AnnotationEnhancer> enhancersMap =
                    this.applicationContext.getBeansOfType(AnnotationEnhancer.class, false, false);
            if (enhancersMap.size() > 0) {
                List<AnnotationEnhancer> enhancers = enhancersMap.values()
                        .stream()
                        .sorted(new OrderComparator())
                        .collect(Collectors.toList());
                this.enhancer = (attrs, element) -> {
                    Map<String, Object> newAttrs = attrs;
                    for (AnnotationEnhancer enh : enhancers) {
                        newAttrs = enh.apply(newAttrs, element);
                    }
                    return attrs;
                };
            }
        }
    }

    private RocketMQMessageListener enhance(AnnotatedElement element, RocketMQMessageListener ann) {
        if (this.enhancer == null) {
            return ann;
        } else {
            return AnnotationUtils.synthesizeAnnotation(
                    this.enhancer.apply(AnnotationUtils.getAnnotationAttributes(ann), element), RocketMQMessageListener.class, null);
        }
    }

    public interface AnnotationEnhancer extends BiFunction<Map<String, Object>, AnnotatedElement, Map<String, Object>> {
    }
}

RocketMQMessageListenerBeanPostProcessor实现了ApplicationContextAware、BeanPostProcessor、InitializingBean接口，其中postProcessAfterInitialization方法判断bean有没有RocketMQMessageListener注解，如果有的话则通过enhance进行增强，另外会通过listenerContainerConfiguration的registerContainer进行注册
其afterPropertiesSet方法会执行buildEnhancer方法，该方法会获取AnnotationEnhancer的bean实例，然后排序好，最后构造AnnotationEnhancer，其作用就是把这些enhancers挨个apply上去

registerContainer

rocketmq-spring-boot/src/main/java/org/apache/rocketmq/spring/autoconfigure/ListenerContainerConfiguration.java

    public void registerContainer(String beanName, Object bean, RocketMQMessageListener annotation) {
        Class<?> clazz = AopProxyUtils.ultimateTargetClass(bean);

        if (RocketMQListener.class.isAssignableFrom(bean.getClass()) && RocketMQReplyListener.class.isAssignableFrom(bean.getClass())) {
            throw new IllegalStateException(clazz + " cannot be both instance of " + RocketMQListener.class.getName() + " and " + RocketMQReplyListener.class.getName());
        }

        if (!RocketMQListener.class.isAssignableFrom(bean.getClass()) && !RocketMQReplyListener.class.isAssignableFrom(bean.getClass())) {
            throw new IllegalStateException(clazz + " is not instance of " + RocketMQListener.class.getName() + " or " + RocketMQReplyListener.class.getName());
        }

        String consumerGroup = this.environment.resolvePlaceholders(annotation.consumerGroup());
        String topic = this.environment.resolvePlaceholders(annotation.topic());

        boolean listenerEnabled =
            (boolean) rocketMQProperties.getConsumer().getListeners().getOrDefault(consumerGroup, Collections.EMPTY_MAP)
                .getOrDefault(topic, true);

        if (!listenerEnabled) {
            log.debug(
                "Consumer Listener (group:{},topic:{}) is not enabled by configuration, will ignore initialization.",
                consumerGroup, topic);
            return;
        }
        validate(annotation);

        String containerBeanName = String.format("%s_%s", DefaultRocketMQListenerContainer.class.getName(),
            counter.incrementAndGet());
        GenericApplicationContext genericApplicationContext = (GenericApplicationContext) applicationContext;

        genericApplicationContext.registerBean(containerBeanName, DefaultRocketMQListenerContainer.class,
            () -> createRocketMQListenerContainer(containerBeanName, bean, annotation));
        DefaultRocketMQListenerContainer container = genericApplicationContext.getBean(containerBeanName,
            DefaultRocketMQListenerContainer.class);
        if (!container.isRunning()) {
            try {
                container.start();
            } catch (Exception e) {
                log.error("Started container failed. {}", container, e);
                throw new RuntimeException(e);
            }
        }

        log.info("Register the listener to container, listenerBeanName:{}, containerBeanName:{}", beanName, containerBeanName);
    }

ListenerContainerConfiguration的registerContainer方法会根据注解信息及对应的bean构造DefaultRocketMQListenerContainer并注册到genericApplicationContext，同时执行其start方法

DefaultRocketMQListenerContainer

rocketmq-spring-boot/src/main/java/org/apache/rocketmq/spring/support/DefaultRocketMQListenerContainer.java

public class DefaultRocketMQListenerContainer implements InitializingBean,
    RocketMQListenerContainer, SmartLifecycle, ApplicationContextAware {

    private DefaultMQPushConsumer consumer;

    private RocketMQListener rocketMQListener;

    @Override
    public void start() {
        if (this.isRunning()) {
            throw new IllegalStateException("container already running. " + this.toString());
        }

        try {
            consumer.start();
        } catch (MQClientException e) {
            throw new IllegalStateException("Failed to start RocketMQ push consumer", e);
        }
        this.setRunning(true);

        log.info("running container: {}", this.toString());
    }

    @Override
    public void afterPropertiesSet() throws Exception {
        initRocketMQPushConsumer();

        this.messageType = getMessageType();
        this.methodParameter = getMethodParameter();
        log.debug("RocketMQ messageType: {}", messageType);
    }

    private void initRocketMQPushConsumer() throws MQClientException {
        if (rocketMQListener == null && rocketMQReplyListener == null) {
            throw new IllegalArgumentException("Property 'rocketMQListener' or 'rocketMQReplyListener' is required");
        }
        Assert.notNull(consumerGroup, "Property 'consumerGroup' is required");
        Assert.notNull(nameServer, "Property 'nameServer' is required");
        Assert.notNull(topic, "Property 'topic' is required");

        RPCHook rpcHook = RocketMQUtil.getRPCHookByAkSk(applicationContext.getEnvironment(),
            this.rocketMQMessageListener.accessKey(), this.rocketMQMessageListener.secretKey());
        boolean enableMsgTrace = rocketMQMessageListener.enableMsgTrace();
        if (Objects.nonNull(rpcHook)) {
            consumer = new DefaultMQPushConsumer(consumerGroup, rpcHook, new AllocateMessageQueueAveragely(),
                enableMsgTrace, this.applicationContext.getEnvironment().
                resolveRequiredPlaceholders(this.rocketMQMessageListener.customizedTraceTopic()));
            consumer.setVipChannelEnabled(false);
        } else {
            log.debug("Access-key or secret-key not configure in " + this + ".");
            consumer = new DefaultMQPushConsumer(consumerGroup, enableMsgTrace,
                this.applicationContext.getEnvironment().
                    resolveRequiredPlaceholders(this.rocketMQMessageListener.customizedTraceTopic()));
        }
        consumer.setNamespace(namespace);

        String customizedNameServer = this.applicationContext.getEnvironment().resolveRequiredPlaceholders(this.rocketMQMessageListener.nameServer());
        if (customizedNameServer != null) {
            consumer.setNamesrvAddr(customizedNameServer);
        } else {
            consumer.setNamesrvAddr(nameServer);
        }
        if (accessChannel != null) {
            consumer.setAccessChannel(accessChannel);
        }

        consumer.setConsumeThreadMax(consumeThreadMax);
        consumer.setConsumeThreadMin(consumeThreadNumber);
        consumer.setConsumeTimeout(consumeTimeout);
        consumer.setMaxReconsumeTimes(maxReconsumeTimes);
        consumer.setAwaitTerminationMillisWhenShutdown(awaitTerminationMillisWhenShutdown);
        consumer.setInstanceName(instanceName);
        switch (messageModel) {
            case BROADCASTING:
                consumer.setMessageModel(org.apache.rocketmq.remoting.protocol.heartbeat.MessageModel.BROADCASTING);
                break;
            case CLUSTERING:
                consumer.setMessageModel(org.apache.rocketmq.remoting.protocol.heartbeat.MessageModel.CLUSTERING);
                break;
            default:
                throw new IllegalArgumentException("Property 'messageModel' was wrong.");
        }

        switch (selectorType) {
            case TAG:
                consumer.subscribe(topic, selectorExpression);
                break;
            case SQL92:
                consumer.subscribe(topic, MessageSelector.bySql(selectorExpression));
                break;
            default:
                throw new IllegalArgumentException("Property 'selectorType' was wrong.");
        }

        switch (consumeMode) {
            case ORDERLY:
                consumer.setMessageListener(new DefaultMessageListenerOrderly());
                break;
            case CONCURRENTLY:
                consumer.setMessageListener(new DefaultMessageListenerConcurrently());
                break;
            default:
                throw new IllegalArgumentException("Property 'consumeMode' was wrong.");
        }

        //if String is not is equal "true" TLS mode will represent the as default value false
        consumer.setUseTLS(new Boolean(tlsEnable));

        if (rocketMQListener instanceof RocketMQPushConsumerLifecycleListener) {
            ((RocketMQPushConsumerLifecycleListener) rocketMQListener).prepareStart(consumer);
        } else if (rocketMQReplyListener instanceof RocketMQPushConsumerLifecycleListener) {
            ((RocketMQPushConsumerLifecycleListener) rocketMQReplyListener).prepareStart(consumer);
        }

    }
    //......
}    

DefaultRocketMQListenerContainer的start方法(SmartLifecycle)执行consumer的start方法；其afterPropertiesSet方法(InitializingBean)会执行initRocketMQPushConsumer方法来创建consumer
initRocketMQPushConsumer方法主要是创建DefaultMQPushConsumer，设置messageModel，根据selectorType执行subscribe方法，根据consumeMode来设置messageListener(DefaultMessageListenerOrderly或者DefaultMessageListenerConcurrently)，最后针对RocketMQPushConsumerLifecycleListener执行prepareStart方法

DefaultMessageListenerOrderly

rocketmq-spring-boot/src/main/java/org/apache/rocketmq/spring/support/DefaultRocketMQListenerContainer.java

    public class DefaultMessageListenerOrderly implements MessageListenerOrderly {

        @SuppressWarnings("unchecked")
        @Override
        public ConsumeOrderlyStatus consumeMessage(List<MessageExt> msgs, ConsumeOrderlyContext context) {
            for (MessageExt messageExt : msgs) {
                log.debug("received msg: {}", messageExt);
                try {
                    long now = System.currentTimeMillis();
                    handleMessage(messageExt);
                    long costTime = System.currentTimeMillis() - now;
                    log.debug("consume {} cost: {} ms", messageExt.getMsgId(), costTime);
                } catch (Exception e) {
                    log.warn("consume message failed. messageId:{}, topic:{}, reconsumeTimes:{}", messageExt.getMsgId(), messageExt.getTopic(), messageExt.getReconsumeTimes(), e);
                    context.setSuspendCurrentQueueTimeMillis(suspendCurrentQueueTimeMillis);
                    return ConsumeOrderlyStatus.SUSPEND_CURRENT_QUEUE_A_MOMENT;
                }
            }

            return ConsumeOrderlyStatus.SUCCESS;
        }
    }

DefaultMessageListenerOrderly实现了MessageListenerOrderly的consumeMessage接口，它内部遍历msgs，挨个执行handleMessage，有异常的话则设置context.setSuspendCurrentQueueTimeMillis(suspendCurrentQueueTimeMillis)，然后返回ConsumeOrderlyStatus.SUSPEND_CURRENT_QUEUE_A_MOMENT

DefaultMessageListenerConcurrently

rocketmq-spring-boot/src/main/java/org/apache/rocketmq/spring/support/DefaultRocketMQListenerContainer.java

    public class DefaultMessageListenerConcurrently implements MessageListenerConcurrently {

        @SuppressWarnings("unchecked")
        @Override
        public ConsumeConcurrentlyStatus consumeMessage(List<MessageExt> msgs, ConsumeConcurrentlyContext context) {
            for (MessageExt messageExt : msgs) {
                log.debug("received msg: {}", messageExt);
                try {
                    long now = System.currentTimeMillis();
                    handleMessage(messageExt);
                    long costTime = System.currentTimeMillis() - now;
                    log.debug("consume {} cost: {} ms", messageExt.getMsgId(), costTime);
                } catch (Exception e) {
                    log.warn("consume message failed. messageId:{}, topic:{}, reconsumeTimes:{}", messageExt.getMsgId(), messageExt.getTopic(), messageExt.getReconsumeTimes(), e);
                    context.setDelayLevelWhenNextConsume(delayLevelWhenNextConsume);
                    return ConsumeConcurrentlyStatus.RECONSUME_LATER;
                }
            }

            return ConsumeConcurrentlyStatus.CONSUME_SUCCESS;
        }
    }

DefaultMessageListenerConcurrently实现了MessageListenerConcurrently接口的consumeMessage方法，它内部遍历msgs，挨个执行handleMessage，有异常的话设置context.setDelayLevelWhenNextConsume(delayLevelWhenNextConsume)，然后返回ConsumeConcurrentlyStatus.RECONSUME_LATER

handleMessage

    private void handleMessage(
        MessageExt messageExt) throws MQClientException, RemotingException, InterruptedException {
        if (rocketMQListener != null) {
            rocketMQListener.onMessage(doConvertMessage(messageExt));
        } else if (rocketMQReplyListener != null) {
            Object replyContent = rocketMQReplyListener.onMessage(doConvertMessage(messageExt));
            Message<?> message = MessageBuilder.withPayload(replyContent).build();

            org.apache.rocketmq.common.message.Message replyMessage = MessageUtil.createReplyMessage(messageExt, convertToBytes(message));
            DefaultMQProducer producer = consumer.getDefaultMQPushConsumerImpl().getmQClientFactory().getDefaultMQProducer();
            producer.setSendMsgTimeout(replyTimeout);
            producer.send(replyMessage, new SendCallback() {
                @Override public void onSuccess(SendResult sendResult) {
                    if (sendResult.getSendStatus() != SendStatus.SEND_OK) {
                        log.error("Consumer replies message failed. SendStatus: {}", sendResult.getSendStatus());
                    } else {
                        log.debug("Consumer replies message success.");
                    }
                }

                @Override public void onException(Throwable e) {
                    log.error("Consumer replies message failed. error: {}", e.getLocalizedMessage());
                }
            });
        }
    }

handleMessage方法则是委托给了rocketMQListener.onMessage(doConvertMessage(messageExt))，即回调业务自定义的RocketMQListener

start

org/apache/rocketmq/client/consumer/DefaultMQPushConsumer.java

    /**
     * This method gets internal infrastructure readily to serve. Instances must call this method after configuration.
     *
     * @throws MQClientException if there is any client error.
     */
    @Override
    public void start() throws MQClientException {
        setConsumerGroup(NamespaceUtil.wrapNamespace(this.getNamespace(), this.consumerGroup));
        this.defaultMQPushConsumerImpl.start();
        if (null != traceDispatcher) {
            try {
                traceDispatcher.start(this.getNamesrvAddr(), this.getAccessChannel());
            } catch (MQClientException e) {
                log.warn("trace dispatcher start failed ", e);
            }
        }
    }

DefaultMQPushConsumer的start方法先执行setConsumerGroup，然后委托给了defaultMQPushConsumerImpl.start()，如果有traceDispatcher的话，则执行traceDispatcher.start方法
defaultMQPushConsumerImpl.start()方法会触发MQClientInstance.start()，后者会触发pullMessageService.start()以及rebalanceService.start()(会在doRebalance的时候触发defaultMQPushConsumerImpl.executePullRequestImmediately，往pullRequestQueue放pullRequest)，前者会从pullRequestQueue获取pullRequest然后执行DefaultMQPushConsumerImpl.pullMessage方法，里头是执行pullAPIWrapper.pullKernelImpl，然后通过pullCallback往processQueue.putMessage，再触发consumeMessageService.submitConsumeRequest，它会回调listener.consumeMessage来消费消息

小结

RocketMQMessageListenerBeanPostProcessor实现了ApplicationContextAware、BeanPostProcessor、InitializingBean接口，其中postProcessAfterInitialization方法判断bean有没有RocketMQMessageListener注解，如果有的话则通过enhance进行增强，另外会通过listenerContainerConfiguration的registerContainer进行注册

ListenerContainerConfiguration的registerContainer方法会根据注解信息及对应的bean构造DefaultRocketMQListenerContainer并注册到genericApplicationContext，同时执行其start方法
DefaultRocketMQListenerContainer的start方法(SmartLifecycle)执行consumer的start方法；其afterPropertiesSet方法(InitializingBean)会执行initRocketMQPushConsumer方法来创建consumer
start方法主要是执行pullMessageService.start()以及rebalanceService.start()，前者负责从pullRequestQueue获取pullRequest然后拉取消息放到processQueue，然后触发回调listener.consumeMessage来消费消息；后者负责rebalance，一开始会触发defaultMQPushConsumerImpl.executePullRequestImmediately，即往pullRequestQueue放pullRequest
pushConsumer本质上还是基于pull的模式来的，从RocketMQMessageListenerBeanPostProcessor --> DefaultRocketMQListenerContainer.start --> DefaultMQPushConsumer.start --> defaultMQPushConsumerImpl.start() --> pullMessageService.start()以及rebalanceService.start()